ddMultDouble1
Returns the product of a double-double-precision floating point number and a double.
slower than ALGORITHM 8 (one call to fastTwoSum more) but about 2x more accurate
relative error bound: 1.5u^2 + 4u^3, i.e. fl(a+b) = (a+b)(1+ϵ), where ϵ <= 1.5u^2 + 4u^3, u = 0.5 * Number.EPSILON
the bound is very sharp
probably prefer
ddMultDouble2due to extra speedALGORITHM 7 of https://hal.archives-ouvertes.fr/hal-01351529v3/document
Parameters
y
a double
x
a double-double precision floating point number